This invention relates to the art of forming powder images and, more particularly, to heat and pressure belt fuser apparatus wherein images are formed directly on the fuser belt or transferred thereto for subsequent transfusing thereof to a final substrate.
In the art of xerography or other similar image reproducing arts, a latent electrostatic image is formed on a charge-retentive surface which may comprise a photoconductor which generally comprises a photoconductive insulating material adhered to a conductive backing. When the image is formed on a photoconductor, the photoconductor is first provided with a uniform charge after which it is exposed to a light image of an original document to be reproduced. The latent electrostatic images, thus formed, are rendered visible by applying any one of numerous pigmented resins specifically designed for this purpose.
It should be understood that for the purposes of the present invention the latent electrostatic image may be formed by means other than by the exposure of an electrostatically charged photosensitive member to a light image of an original document. For example, the latent electrostatic image may be generated from information electronically stored or generated, and this information in digital form may be converted to alphanumeric image by image generation electronics and optics. However, such image generation electronic and optic devices form no part of the present invention.
In the case of a reusable photoconductive surface, the pigmented resin, more commonly referred to as toner which forms the visible images is transferred to a substrate such as plain paper. After transfer the images are made to adhere to the substrate using a fuser apparatus.
The toned image layer may alternately be formed by an ionographic imaging process. In an ionographic imaging process, a latent image is formed on a dielectric image receptor or electroreceptor by ion deposition, as described, for example, in U.S. Pat. Nos. 3,564,556, 3,611,419, 4,240,084, 4,569,584, 4,408,214, 4,365,549, 4,267,556, 4,160,257, and 4,155,093. Generally, the ionographic process entails the use of an ionographic writing head for application of charge in an imagewise pattern on a dielectric receiver t hat retains the charged image. The image is subsequently developed with a developer capable of developing charge images. The toned image layer may then undergo further processing and, finally, be simultaneously transferred and fused to a recording medium, such as paper.
Regardless of the imaging process used, it may be used to develop black, single color, or multi-color images. Multi-color imaging may be done either as a fully formed image or a step formed image. A fully formed image implies that an image with multiple colors is fully formed on the image receptor and then transferred to the recording medium in a single step. In a step formed image the colored toner images are individually formed on the image recorder and transferred to the recording medium one color at a time. Processes for forming monochromatic or polychromatic electrostatic images are disclosed, for example, in U.S. Pat. Nos. 3,672,887, 3,687,661, 4,395,472, 4,353,970, 4,403,848, and 4,286,031. Also, color images may be formed as images on images or images next to images.
U.S. patent application Ser. No. D/93506 (Attorney's Docket No.) which is assigned to the same assignee as the instant invention relates to a belt fuser wherein three fuser rollers cooperate with a pressure roller to form an extended fusing zone through which a substrate carrying toner images passes with the toner images contacting fusing belt. Electrical power is applied to the three contact rolls in such a manner that only the portions of the belt in the fusing zone are heated. Thus, the energy is concentrated only in the part of the fusing belt where it is needed for fusing the toner images on the final substrate. Thus, the free extent of the belt or in other words the portion of the belt outside of the fusing zone remains unheated.
To ensure good electrical contact in the presence of silicone oil contamination on the inner surface of the fusing belt, the contact rollers are textured by knurling bead blasting or any other suitable means. The use of textured rollers improves the electrical contact between the rollers and the resistive layer of the belt. Also, it circumvents the adverse affects that the silicone has on smooth surfaced rolls.
U.S. patent application Ser. No. D/93507 (Attorney's Docket No.) which is assigned to the same assignee as the instant invention relates to belt fuser wherein three fuser rollers cooperate with a pressure roller to form an extended fusing zone through which a belt with resistive substrate or resistive inner coating carrying toner images passes with the toner images contacting the fusing belt. Electrical power is applied to the three fuser rolls in such a manner that only the portions of the belt in the fusing zones are heated to a predetermined operating temperature. The free extent of the belt or in other words the portion of the belt outside of the fusing zone is adapted to be heated to various operating temperatures in order to produce prints with different gloss levels.
U.S. patent application Ser. No. D/93508 (Attorney's Docket No.) which is assigned to the same assignee as the instant invention relates to a power controller which does not rely on the use of sensors such as thermistors to control the operating temperature of a belt fuser. It features various preset inputs to control steady state watts/in, cold start boost watts/in, warmup and cooldown time constants.
The controller sets the desired power based on the on-off cycling of the system. There are no sensors used to measure fuser temperature. For a cold start, the steady state plus boost power is used, during warmup the boost level is exponentially decreased at a rate set by a warmup time constant. When at rest (with no applied power) the power setpoint is exponentially increased at a rate set by a cooldown time constant.
U.S. patent application Ser. No. D/92622 (Attorney's Docket No.) which is assigned to the same assignee as the instant invention relates to a belt fuser for fusing transparencies without having to resort to off-line methods and apparatus. The toner images which are formed on the transparency during the imaging process have time to cool prior to separation from a smooth-surfaced belt.
U.S. patent application Ser. No. D/92623 (Attorney's Docket No.) which is assigned to the same assignee as the instant invention relates to a belt fuser wherein tree fuser rollers cooperate with a pressure roller to form an extended ruling zone through which a belt with resistive substrate or resistive inner coating carrying toner images passes with the toner images contacting fusing belt. Electrical power is applied to the three fuser rolls in such a manner that only the portions of the belt in the focusing zone are heated. Thus, the energy is concentrated only in the part of the fusing belt where it is needed for fusing the toner images on the final substrate. Thus, the free extent of the belt or in other words the portion of the belt outside of the fusing zone remains unheated.
U.S. Pat. No. 5,212,526 granted to Domoto, et. al. on May 18, 1993 relates a method of transferring images from an image receptor to a recording medium, which method comprises forming a toned image layer on a surface of an image receptor, the toned image layer comprising a toner material and a radiation curable material; contacting a recording medium with the toned image layer; and irradiating the toned image layer in contact with the recording medium to cure said radiation curable material; wherein the resulting cured material has greater adhesion to the toner material and the recording medium than to the surface of the image receptor. The radiation is transmitted through the image receptor and onto the toned image layer to cure the radiation curable material.
U.S. Pat. No. 5,103,263 granted to Moore et al on Apr. 7, 1992 relates to a photoconductive or magnetic filler which allows a single thin belt to serve as the imaging element, i.e., as the latent and developed image carrier, as well as the element which transfers and fuses toner to a print. The transport member moves in a cyclic path to carry material from a first location to a second location maintained at a higher temperature, and counter-moving portions of the member are positioned to exchange heat with each other along an intermediate portion of the path, so that minimum energy is lost to the environment. In one embodiment as a printing apparatus, a be It transports a heat-fusible toner to a heated location where it is transferred and fused, i.e., as a print image to a sheet. Effective powder pick up and release is obtained in the printing apparatus with a transport member having an elastomeric layer of a softness which conforms to a receiving member of characteristic surface roughness, and a non-tacky outer coating which is harder than the elastomeric layer. The location at the lower temperature is maintained in a preset operating range by a cooler or ventilator. The higher temperature location is maintained at the higher temperature by a heater.
In the field of photocopying or printing, it is known to print by first forming an electrostatic latent image on a photoconductive drum or belt, developing the electrostatic latent image on the drum with a toner, and then transferring the toner to a moving belt which carries the toner past a heat fusing station where the toner is melted and transferred to paper or some other print substrate. Systems of this type are shown in U.S. Pat. Nos. 3,893,761; 3,923,392 and 3,947,113. Such a system has been made and marketed commercially. In the commercial system known to applicant, the belt transports developed toner images to a high temperature fusing and transfer station. The belt is relatively thick, e.g., one or more millimeters thick, that is operated isothermally at a temperature over 100.degree. Celsius which is sufficient to fuse the transported toner. In such a construction, the belt serves to isolate the primary latent-image forming member, which is a photoconductive belt, from the high fusing temperatures allowing the photoconductive belt to operate with conventional powdered toner image development technologies.
Such a construction results in a complex assembly wherein a first image forming and toner transport mechanism is operated at one temperature, and a comparably large transport assembly is maintained at a higher temperature within the machine. The machine requires a significant power input for its healed portion, and is mechanically complex. The transfer of toner between two or more intermediate members adversely affects image quality, particularly if the intermediate members are heated.
Accordingly, it would be desirable in systems of this sort to simplify the mechanical structure, reduce the power requirements, and improve the image transfer characteristics.
It is an object of the invention to provide an efficient image forming apparatus wherein a toner image is formed at one location on an unheated segment of a combination fusing and image receptor belt and then at a second location where the belt is heated to simultaneously transfer and fuse the toner image from the combination belt to a substrate to form a print.